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Information about glaciers

Published on December 23, 2008

Author: aSGuest7971


Slide 1: GLACIERS Quick Glacier Facts: : Quick Glacier Facts: Glaciers are masses of ice that flow under the influence of gravity. Glaciers cover about 10% of the Earth's land surface, with the Greenland and Antarctica ice sheets accounting for about 96% of the land covered. Glaciers are the largest reservoir of fresh water and contain about 2.15% of the world's water. Mountain/Alpine glaciers are found all over the world, even near the equator. Glacial ice eventually melts or vaporizes and returns to the hydrologic cycle. GLACIERS : GLACIERS A mass of ice that originates on land, usually having an area larger than one tenth of a square kilometer. 2 Basic Types: Alpine, Valley or Mountain glaciera glacier that is confined by surrounding mountain terrain. Continental glaciers or Ice Sheets: glaciers that are unconfined by topography, they form at high latitudes where temperatures remain cold enough during the summer to keep the previous winter's snow from melting allowing snow and ice to accumulate. Slide 4: Valley Glacier Continental Glacier : Continental Glacier Slide 6: Accumulation: all processes by which snow or ice are added to a glacier, this is typically the accumulation of snow, which is slowly transformed into ice; other accumulation processes can include avalanches, wind-deposited snow, and the freezing of rain within the snow pack. Accumulation zone: area of a glacier where more mass is gained than lost. GLACIERS: VOLCABULARY Ablation: combined processes which remove snow or ice from the surface of a glacier or from a snow-field; also used to express the quantity lost by these processes. Ablation area: the area of a glacier where more glacier mass is lost than gained Terminus: the lowest end of a glacier; also called glacier snout or toe. : Terminus: the lowest end of a glacier; also called glacier snout or toe. Slide 8: The snow that eventually makes up ice sheet and glaciers undergoes a sequence of conversion stages 1-snow fall : feathery - mainly air 2-settling of snow: loose granular consistency as the crystals begin to break up on collapse, and with the weight of overlying snow, plus partial melting 3-nivation: annual and diurnal temperature changes lead to thaw-freeze alternation and the conversion of snow into ice crystals 4-firn (or neve) - increased pressure between individual grains causes pressure melting to eventually change the loose snow into a dull, white structure-less mass with far less pore space (takes at least one year) 5-sintering - continued fusion and squeezing out of air as a result of compression by further accumulation 6- glacier ice - bluish in colour and containing little air - this may take 40-50 years, depending on the location The Formation of Glacial Ice: Slide 9: ICE: Has well developed crystalline structure and displays internal pattern of thin layers, each layer representing a year’s accumulation of snow. Crystals are platy, and can be compressed more because of the shape. Glacial Erosion and Transport : Glacial Erosion and Transport Plucking (Quarrying) - similar to frost wedging. Meltwater penetrates into bedrock cracks and refreezes, prying angular blocks of rock loose. These blocks may be incorporated into the ice, producing boulders known as glacial erratics which may be transported long distances. Abrasion - rock fragments carried by ice function as "sandpaper" that scours the surface over which the ice moves. This process produces rock flour (very fine particles of pulverized rock), striations (long grooves and scratches cut into bedrock), and glacial polish (a very smooth surface produced by fine abrasion of bedrock by rock flour). Bulldozing - glacier pushes loose material in its path. Erosional Features : Erosional Features Slide 12: Valley Glaciers are associated with: 1- U-shaped valleys 2- Paternoster lakes 3- Fiords/ Fjords 4- Hanging valleys 5- Cirques 6- Horns 7- Aretes Slide 13: Continental Glaciers are associated with: Land, smoothed and rounded from glacial abrasion, produces a flattened topography with rounded hills. Erosion strips soil and sediment away to expose bedrock, producing ice-scoured plains. Stream drainage patterns are disrupted, producing deranged drainage patterns with numerous lakes and swamps Slide 14: Slide 15: Hanging valley: a valley formed by a small glacier that has a valley bottom relatively higher than nearby valleys formed by larger glaciers. Horn: a peak or pinnacle thinned and eroded by three or more glacial cirques. Arete: sharp, narrow ridge formed as a result of glacial erosion from both sides. Slide 17: Cirque: bowl shape or amphitheater usually sculpted out of the mountain terrain by a cirque glacier. cirque glacierglacier that resides in basins or amphitheaters near ridge crests; most cirque glaciers have a characteristic circular shape, with their width as wide or wider than their length. U-Shaped Valleys: : U-Shaped Valleys: characteristic shape of glaciated valleys, as opposed to characteristic V-shape of stream valleys. Glaciers follow pre-existing stream valleys, making them broader and deeper. Outwash: Glacial Melt water : Outwash: Glacial Melt water Slide 20: Paternoster lakes - produced when water fills rock basins (bedrock depressions produced by glacial plucking) in the valley floor. Fiords - deep sea inlets formed by the flooding of glacial valleys. Restricted to high latitudes, they can be up to 1,300 meters deep. Depositional Features : Depositional Features Glacial Deposits: Glacial Sediments : Glacial Deposits: Glacial Sediments Till - unsorted, unlayered material deposited directly by a glacier. Landforms composed of till include: 1- Moraines 2-Drumlins 3-Glacial Erratics Stratified drift - sorted, stratified sediment laid down by glacial meltwater (often by braided streams). Landforms composed of stratified drift and deposited by glacial meltwater include: 1-Outwash Plains 2- Kettles 3- Kames 4- Eskers 5- Varves Till: : Till: unsorted, unlayered material deposited directly by a glacier Moraines: : Moraines: morainea mound, ridge, or other distinct accumulation of glacial till. lateral morainea ridge-shaped moraine deposited at the side of a glacier and composed of material eroded from the valley walls by the moving glacier. medial morainea ridge-shaped moraine in the middle of a glacier originating from a rock outcrop, nunatak, or the converging lateral moraines of two or more ice streams. (Nunatak a rocky crag or small mountain projecting from and surrounded by a glacier or ice sheet.) Slide 26: Recessional moraine - a series of end moraines formed by a receding glacier that periodically stabilized. medial moraine - central moraine formed when two valley glaciers merge and combine their lateral moraines. end moraine- an arch-shaped ridge of moraine found near the end of a glacier Slide 28: Ground / dump morainea mound or layer of moraine formed along the edge of a glacier by rock that falls off the ice. Slide 29: Drumlins - Only produced by continental glaciers, these are smooth, elongate, parallel hills of reworked glacial drift that are thought to form when glaciers advance over previously deposited drift. The steep slope faces the direction of glacier advance. Clusters are called drumlin fields. Glacial Erratic : Glacial Erratic A boulder or large block of bedrock transported away from its source by a glacier. Stratified Drift: : Stratified Drift: sorted, stratified sediment laid down by glacial meltwater Slide 32: Sandar also called Outwash Plains: extensive flat plains of sand & gravel (unconstrained by topography) with braided streams of glacial meltwater. Slide 33: Varve:sequence of laminae, deposited in lakes; representing a year's sedimentation Slide 34: A kame is an irregularly shaped hill or mound composed of sorted or stratified sand and gravel that is deposited in contact with the glacial ice. It can have an irregular shape. Kame terraces are frequently found along the side of a glacial valley and are the deposits of meltwater streams flowing between the ice and the adjacent valley side. Kames are often associated with kettles, and this is referred to as kame and kettle topography. : KAME Slide 36: A kettle (or kettle hole) is a landform created by glacial meltwater. They occur as the result of blocks of ice calving from the front of a receding glacier and becoming partially to wholly buried by glacial outwash. When the ice blocks melt, holes are left. Slide 37: Eskerlong, commonly sinuous ridge of sand & gravel; deposited by a stream in a sub-glacial tunnel GLACIAL MOVEMENT : GLACIAL MOVEMENT In general, valley glaciers move faster than continental glaciers Slide 39: Valley Glaciers Rates vary from centimeters per day to tens of meters per day. The steeper the slope, the faster the rate of movement. Larger ice masses move faster than smaller ice masses. Basal slip is most rapid in warmer months and can produce brief periods of rapid movement called surges. Surges can be produced by unusually heavy precipitation and by avalanches loading the upper part of a valley glacier. In a valley glacier, ice moves fastest at the upper center part of zone of plastic flow. Continental Glaciers - average rate of movement is a few cm/day or a few m/day. Flow rates are fastest in the zone of accumulation and decrease below the firn line toward the margins. Thicker ice sheets have higher flow rates than thinner ones. : Continental Glaciers - average rate of movement is a few cm/day or a few m/day. Flow rates are fastest in the zone of accumulation and decrease below the firn line toward the margins. Thicker ice sheets have higher flow rates than thinner ones. These glaciers show little basal slip and may be frozen to the underlying surface. Slide 41: Plastic flow - Under pressure, ice can flow plastically. Glacial movement inside the ice mass takes place by this mechanism (zone of flow). Uppermost part of ice sheet (zone of fracture) is not under pressure and cracks as the ice below it moves, locally producing deep crevasses (cracks). Basal slip - The base of the glacier moves slowest because of friction. Friction produces melt water which lubricates the ice mass, allowing it to slip when under enough pressure. Slide 42: Large Crevasses: Found on the uppermost surface of the glacier. The surface ice cracks as the ice below it flows plastically.

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